单项选择题
The figure shows two cylinders of diameter D and 2D, connected to each other and containing an incompressible fluid. The two cylinders are fitted with leak-proof pistons of weight W1 and W2 as shown. Which of the following is a correct expression?（ ）。
A．
＝
B．
=
C．
=
D．
=
＝B．
=C．
=D．
=
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